Natural rubber vulcanizing composition containing sulfonate esters as scorch retarders and method of vulcanizing same



f nited States Patent fifice 2,851,508 Patented Sept. 9, 1958 Carl A. Uraneck, Phillips, Tex., assignor to Phillips Petroleum ompany, a corporation of Delaware No Drawing. Application July 14, 1953 Serial No. 367,970

15 Claims. (Cl. 260-780) This invention relates to the use of sulfonate esters as scorch retarders in the vulcanization of rubber compounds.

carbon black, black retards the curing action, and scorching is not a particularly serious problem. However, with carbon blacks having a pH above 8 it is usually necessary to employ a scorch retarder in the compounding mixture.

According to our invention, there is provided a method alkyl, cycloalkyl, aryl radical and any combination of these radicals and will contain from 6 to 20 carbon atoms and R is selected from the group consisting of an alkyl,

tiary-butyl 2-phenylhexanesulfonate,

secondary-butyl pethoxybenzenesulfonate,

cyclohexyl diisopropylbenzenebe employed.

My materials dithiocarbamates, mercaptobenzothiazole, benzothiazole disulfide, N-cyclohexyl-Z-benzothiazole sulfenamide, and the like.

The scorching property of a particular rubber mix can be determined by various test methods which are described in the literature. I have employed one of the EXAMPLE Three rubber mixes were preparedaccording to the following compounding recipe. One of these contained no scorch retarder and served as a control while the other two contained methyl p-toluenesulfonate and ethyl ptoluenesulfonate respectively.

Table I Zinc Oxide Stearic Acid. Parafiux Flexamine L Santocure 4 Sulfur Methyl p-toluenesulfonate Ethyl p-toluenesulfonate ropHmcew- 1 High pH furnace carbon black.

9 An asphaltic flux. 3 Physical rnlxture containing wt. percent of a complex diarylamineketone reaction product and 35 wt. percent N ,N '-diphenyl-p-puenylenediemme.

4 N -cyclohexyl-2benzothiazole sulfeuamide.

The Mooney scorch time at 250 F. and other physical natural rubber, a vulcanization accelerator, and an eifecproperties of the above samples were determined and are tive amount of an alkyl aromatic sulfonate in which the recorded in the following table: aromatic portion of the molecule contains 6-20 carbon Table 11 [30 minutes cure time at 307 F.] 80 F. Oven Aged 24 Hrs, 212 F. Scorch at 250 F.

Scorch Retarder 300% Tensile, Elonga- 300% Tensile, Elonga- Compres- Minl- Minutes Modulus, p. s. i. tion, Modulus, p. 3.1. tlon, sion Set, mum to Scorch p. s. 1. percent p. s. 1. percent percent, Mooney None 1 690 3,250 490 1, 740 2,125 340 9 44 Methylp-toluenesulfonate 1, 440 2.950 485 1,465 1, 540 310 28 0 38 19 5 Ethyl p-toluenesulionate 1 590 3,100 480 1, 500 1. 725 340 23 7 as 5 1s The use of the sulfonate' esters increased the scorch time atoms" and in which the alkyl portion of the molecule at 250 F. by 4 /2 and 3 minutes respectively as indicated does not contain more than 16 carbon atoms. in the preceding table. This is an increase of 30 and 20 7. A rubber composition having improved scorch time percent over the scorch time of the control, which con- 2.0 characteristics, said composition containing essentially a tained no scorch retarder. natural rubber, a vulcanization accelerator, and an effec- Reasonable variation and modification are possible e amount of a Sulfonflte ester haVlIlg the followlflg within the scope of the foregoing disclosure and the apformula: pended claims to the invention, the essence of which is that a method for increasing scorch time, i. e., reducing R-S-OR or avoiding procuring during the compounding of rubbers, especially natural rubber, has been provided together with rubber compositions, containing a scorch retarder according to the invention, which compositions exhibit increased scorch times, said scorch retarder being a sulfonate ester, preferably a sulfonate ester as set forth and described herein.

I- claim:

1. A method for increasing the scorch time ora natural rubber composition comprising a vulcanizationaccelerator which comprises incorporating into said composition an effective amount of a scorch retarder selected from the group consisting of compounds having the following formula:

wherein R is selected from the group consisting of an alkyl, cycloalkyl, aryl radical and radicals composed of 30 any combination of these radicals and will contain from 6 to 20 carbon atoms and R is selected from the group consisting of an alkyl, cycloalkyl, and radicals composed of a combination of these radicals and will contain not more than 16 carbon atoms. 8. A rubber composition having improved scorch time characteristics, said composition containing essentially a natural rubber, a vulcanization accelerator, and an effective amount of a methyl p-toluenesulfonate.

9.- A rubber composition having improved scorch time characteristics, said composition containing essentially 9 anatural rubber, a vulcanization accelerator, and an effec- 1 ti ve amount of an ethyl p-toluenesulfonate.

' 10. A method of increasing the scorch time of a rubber composition comprising a vulcanization accelerator wherein R is selected from the group consisting-of an which comprises incorporating into said composition a alkyl, cycloalkyl, aryl radical and radicals composed of methyl naphthalenesulfonate.

any combination of these radicals and will contain from v A method Of increasing the Scorch time of a Illh' 6 to 20 carbon atoms and R is selected from the group ber composition comprising a vulcanization accelerator consisting of an alkyl, cycloalkyl, and radicals composed Which Comprises iHCOIPOIatiHg into said composition an ora combination of these radicals and will contain not yl xylefleslllfoflatemore than 16 carbon atoms. 12. A method of increasing the scorch time of a rub- 2. A method according to claim 1 wherein 0,5 t 5 ber composition comprising a vulcanization accelerator parts per hundred of rubber of the said ester is incorwhich Comprises incorporating into Said composition a porated into said composition. secondary-butyl p-ethoxybenzenesulfonate.

3. A method of increasing the scorch time of a natural A Fhhhef Composition having improved Scorch rubber composition comprising a vulcanization acceleratime characteristics, Said Composition, Containing essentor which comprises incorporating into said composition tially a natural rubber, a Vulcanilation accelerator, and a an efiective amount of an alkyl aromatic sulfonate in methyl flaphthalenesulfonatewhich the aromatic portion of the molecule contains 6- A rubber Composition having improved scorch 20 carbon atoms and in which the alkyl po -{i0 1 f {h time characteristics, said composition containing essenmolecule rims not contain more than 16 carb t tially a natural rubber, a vulcanization accelerator, and

4. A method of increasing the scorch time of a natural ah ethyl Xylenesulfonaterubber composition comprising a vulcanization accelera- A rubber composition having improved Scorch tor which comprises incorporating into said composition il? Characteristics said comPosition Containing essenan ff tiv amount of methyl -t ,l lf t tially a natural rubber, a vulcanization accelerator, and a 5. A method of increasing thescorch time of a natural sigcondary'buwl Fethoxybenzenesulbnaterubber composition comprising a vulcanization accelera- References Cited in the file of this atent tor which comprises incorporating into said composition P an efiective amount of ethylp-toluenesulfonate. UNITED STATES PATENTS 6. A rubber composition having improved scorch time 1,871,037 Cadwell Aug. 9, 1932 characteristics, said composition containing essentially a 2,687,444 Crouch et a1 Aug. 24, 1954 

1. A METHOD FOR INCREASING THRE SORCH TIME OF A NATURAL RUBBER COMPOSITION COMPRISING A VULCANIZATION ACCELERATOR WHICH COMPRISES INCORPORATING INTO SAID COMPOSITION AN EFFECTIVE AMOUNT OF A STORCH RETARDER SELECTED FROM THE GROUP CONSISITNG OF COMPOUNDS HAVING THE FOLLOWING FORMULA: 